ClipArt ETC
"Section of the human eye." — Blaisedell, 1904

Human eye

"Section of the human eye." — Blaisedell, 1904

"The Actual Size of the Test Type, which shiykd be seen by the Normal Eye at a distance of Twenty Feet." — Blaisedell, 1904

Test type

"The Actual Size of the Test Type, which shiykd be seen by the Normal Eye at a distance of Twenty Feet."…

"Suppose the object a, appears to the naked eye of the length repreesnted in the drawing. Now, as the rays coming from each end of the object, form by their convergence at the eye, the visual angle, or the angle under which the object is seem, and we call objects large or small in proportion as this angle is obtuse or acute, if, therefore, the object a be withdrawn futher from the eye, it is apparent that the rays o, o, proceeding from its extremities, will enter the eye under a more acute angle, and therefore that the object will appear diminished in proportion." -Comstock 1850

Visual Angle

"Suppose the object a, appears to the naked eye of the length repreesnted in the drawing. Now, as the…